In woodworking machines which carry changeable rotary tools, it has generally been the practice to secure the tool on the axle shaft by sliding the tool thereon and tightening it by means of a nut threaded onto the axle shaft. Since different woodworking tools have different widths, it has been necessary to use spacers on opposite sides of the tool in order to take up the space between the shoulder of the axle and the closest position of the threaded nut. This has often presented a problem with respect to precisely locating the tool because the axial position of the tool on the axle is dictated by the number and thickness of available spacers.